Bug 1633713 - Set WS_EX_COMPOSITED to PiP window on Windows7 r=jrmuizel

When window is PiP window on Windows7, WS_EX_COMPOSITED is set to suppress flickering during resizing with hardware acceleration as a workaround.

PiP window detection in nsAppShellService::JustCreateTopWindow() mimics Linux/Gtk implementation.

Differential Revision: https://phabricator.services.mozilla.com/D77663

widget/windows/nsWindow.cpp

@@ -838,6 +838,15 @@ nsresult nsWindow::Create(nsIWidget* aParent, nsNativeWidget aNativeParent,
   DWORD style = WindowStyle();
   DWORD extendedStyle = WindowExStyle();
 
+  // When window is PiP window on Windows7, WS_EX_COMPOSITED is set to suppress
+  // flickering during resizing with hardware acceleration.
+  bool isPIPWindow = aInitData && aInitData->mPIPWindow;
+  if (isPIPWindow && !IsWin8OrLater() &&
+      gfxConfig::IsEnabled(gfx::Feature::HW_COMPOSITING) &&
+      WidgetTypeSupportsAcceleration()) {
+    extendedStyle |= WS_EX_COMPOSITED;
+  }
+
   if (mWindowType == eWindowType_popup) {
     if (!aParent) {
       parent = nullptr;

xpfe/appshell/nsAppShellService.cpp

@@ -608,6 +608,19 @@ nsresult nsAppShellService::JustCreateTopWindow(
       ((aChromeMask & pipMask) == pipMask) && !(aChromeMask & barMask)) {
     widgetInitData.mPIPWindow = true;
   }
+#elif defined(XP_WIN)
+  // Windows PIP window support. It's Chrome dialog window, always on top
+  // and without any bar.
+  uint32_t pipMask = nsIWebBrowserChrome::CHROME_ALWAYS_ON_TOP |
+                     nsIWebBrowserChrome::CHROME_OPENAS_CHROME;
+  uint32_t barMask = nsIWebBrowserChrome::CHROME_MENUBAR |
+                     nsIWebBrowserChrome::CHROME_TOOLBAR |
+                     nsIWebBrowserChrome::CHROME_LOCATIONBAR |
+                     nsIWebBrowserChrome::CHROME_STATUSBAR;
+  if (widgetInitData.mWindowType == eWindowType_dialog &&
+      ((aChromeMask & pipMask) == pipMask) && !(aChromeMask & barMask)) {
+    widgetInitData.mPIPWindow = true;
+  }
 #endif
 
 #ifdef XP_MACOSX